Various processes are known for producing sulfur dioxide (SO2) and sulfur trioxide (SO3). Typically the known processes require significant capital outlays because of the very high temperatures involved in the exothermic reaction between sulfur and air or oxygen to form sulfur dioxide. While various methods of reducing the temperatures incurred in the process have been proposed, such methods usually involve complicated, relatively expensive equipment. Most SO2, SO3, and sulfuric acid (H2SO4) plants use air to dilute and reduce the exotherm. Such plants require expensive nitrogen separation and scrubbing equipment. If air is omitted from the process, production of SO2, SO3, and H2SO4 would require sulfur burners with a high temperature operating zone. Because of the operating temperatures of the burners, existing plants require refractory lined after-coolers and/or waste heat boilers. In addition, oftentimes excess gases need to be removed from the gaseous sulfur trioxide products and scrubbed to remove impurities. In some cases, complicated and expensive automated recycling systems are required in previously proposed processes.
A relatively small installation used heretofore for producing SO3 from SO2 is schematically depicted in FIG. 3. Unfortunately, such an installation is limited to the availability of “over the fence” source(s) of SO2 raw material. Therefore the continued ability to produce SO3 is heavily dependent on local sources of economical SO2. Attempts to operate the plants such as depicted in FIG. 3 at overcapacity involving higher-than-designed throughputs from spot sources of SO2 becomes uneconomical. To meet the necessary needs from SO3 then becomes dependent upon purchases of SO3 from outside sources which also can be an uneconomical way of operating.